Method of electroplating and treating cutting edge tools and the like



Patented Nov. 19, 1946 METHOD OF ELECTROPLATING AND TREAT- ING CUTTING EDGE TOOLS AND THE LIKE Axel E. Lundbye, Springfield, Ohio, assignor to Crowell-Collier Publishing Company, Springfield, Ohio, a corporation 01 Delaware No Drawing. Application March 20, 1944,

Serial No, 527,350

7 Claims.

My .invention relates to improvements in methods of plating and treating metal-cuttin tools such as bits, drills, reamers, taps, saws, milling cutters and the like, and has for an ob- Ject the production of tools that give a longer service thanthe aforementioned high speed alloy tool steels and other chromium plated tools heretofore produced.

Another object of the present invention is to provide methods of chromium plating and treating metal-cutting tools made of the cheaper steels to produce tools superior to tools formed of high speed steels and prior chromium-plated tools.

As is well known to those skilled in the art, it is diflicult to provide metal cutting tools with an adherent layer of chromium that will not peel or chip off the tool.

Furthermore when plating cutting tools or other pieces of steel with chromium there has been a tendency for heads to form along their sharp edges, corners or cutting edges, which, of course, destroys the usefulness of the tool.

Another one of the objects, therefore, of the present invention is to so plate and treat a relais especially adaptable for the plating and treatment of cutting tools made of tool steel, which steels are less expensive than high speed alloy tool steels and are available in much larger quantity.

Referring now more specifically to the preferred plating bath, I take 50 ounces of chromium trioxide (99%%), CrOs,-to which is added /2 ounce (one one-hundredth of the weight of the chromium) of concentrated sulphuric acid (H2SO4) or an equivalent amount of a sulphate salt and dissolve in water to make 1 U. S. gallon of the solution.

Another highly satisfactory bath may contain 33 ounces of chromium trioxide (99%%) and .33 ounce of sulphuric acid or its sulphate equivalent per gallon of solution.

It will be understood that good results can be obtained by using from 30 to 80 ounces of chromium trioxide and a proportional amount of sulphate per gallon of solution.

Other grades than 99%% chromium trioxide can be used, but when another grade or purity of chromium trioxide is used, allowance must again be made for the sulphate (S04) content of the chromium trioxide.

The temperature at which the plating bath is used may be approximately 150 F., as I have found that keeping the bath at this temperature, it is possible to deposit the chromium much more slowly than if the temperature of the bath were lower, and by so doing I find that beads do not form along the cutting edges of the tools. However, good results have been obtained with the temperature ranging from F. to 190 F.

I have also found that the current densities for plating with a bath containing about 50 ounces of chromium trioxide and 0.5 ounce H2304 per gallon may range from 170 to amperes per square foot, although good results may be obtained with a current density ranging from 400 amperes down to the point where chromium will still deposit from the solution. When using less concentrated plating baths, somewhat higher current densities may be used successfully. For example, with a bath containing 33 ounces of chromium trioxide and .33 of H2804 per gallon,

the best results are obtained by using a current density between 0.7 and 3.5 amperes per square inch of cathode (100 to 504 amperes per square foot), and maintaining the temperature of the bath between about 130 and F.

' As an example of my improved method, a bit formed of Molite, a molybdenum tool steel, is first ground and then rubbed down with a fine stone to give a fine and smooth finished edge along the cutting area.

This grinding and stoning operation. also serves to clean the steel for the application of the chromium. After degreasing, the cutting edge of the tool is then dipped in a 10% hydrochloric acid for about 30 seconds, and then well rinsed in cold water, but other cleaning methods may be used.

When the chromium plating bath is ready to be operated, the tool is placed into the solution above mentioned as the cathode to a depth of approximately 4 inch above the cutting edge. The anod preferably used is stainless steel, although a lead anode (90% lead (Pb) and 10% antimony (Sb)) has beenusecl with good results. The size of the anode, of course, is governed by the article to be plated.

The current in the first step is reversed at about amperes per square foot, making thetool to be plated the anode for about 7 seconds, QL' unt l the surface of the tool is slightly etched.

At the end of 7 seconds, the current is reversed, and when this is done the current is adjusted to a current density at which the chromium is plated smoothly and evenly on the tool, and the plating then proceeds for a definite period of time. When using a bath containing 50 ounces of chromium trioxide and .5 ounce of sulphuric acid .per gallon, a current density of H about 130 amperes per square foot is very satisfactory.

I have found that the time for plating should be about 1 to 2 minutes in order to deposit thestrongly adherent but extremely thin plate that is required for best results.

At this point it'might be mentioned that the tool may then be subjected to the heat treatment about to be described or the tool may be subjected to a reversal of current andthen subjected to the heat treatment that follows.

I prefer to subject the tool to a reversal of current before removing it from the bath and if this method is to be used the plating is allowed to proceed for one or two seconds longer than if the current isnot to be reversed.

When the current is reversed before removing the tool from the bath it is also desirable to increase it slightly. This step of the reversal of current and the increase in amperage should only continue for two or three seconds.

I have found that by increasing and reversing the current for two or three seconds before removing the tool from the bath a very smooth bright surface of the chromium results along the cutting edge and any minute beads that might be formed thereon are removed.

This bright smooth deposit presents a better cutting edge and apparently reduces the frictional coefiicient between the tool and the material being worked on, when the tool is in use.

I also believe that inasmuch as hydrogen is absorbed with the chrome upon the base metal that a sudden reversal of the current will release some of this hydrogen, thus assisting in the more complete removal when placed in the oil bath about to be described.

When the chromium is deposited under the conditions and for the time indicated above, a very thin, non-porous, semi-lustrous, blue-white plate is formed on the tool. Metallographic study of the chromium plate shows that the maximum thickness of the plate is about .0001 of an inch, even when utilizing baths and current densities in the above ranges under conditions most favorable for chromium deposition. Under conditions such that less chromium isdeposited, but still within the ranges specified above, the average thickness of the plate may be as little as .000015 inch.

After the bit or tool has been plated, it should be removed from the bath and rinsed well in cold water and dried immediately. It is then transferred to an oil bath which should be kept at a temperature of about 350 R, where it should remain for about 1 hour, after which it should be removed and allowed to cool at room temperature Although an oil bath at 350 F. is probably the most desirable, good results have been obtained with a bath having somewhat higher or lower temperatures.

Furthermore the plated tool may be treated by placing it in brine solution under pressure or in a low melting metal, say lead or tin, or a suitable alloy maintained at the temperature indicated above.

It is thought that the hot oil bath releases some hydrogen which has been plated along with the chromium and thus'decreases-the brittleness of the deposit.

I have found in actual practice that by treating the plated bit as above mentioned, the plating does not peel from the article and that a relatively cheap tool bit so treated, can be put in service and worked continuously for 18 hours without being reground, whereas for the same type of work, the more expensive bits, such as "Stellite bits had to be reground at least ten times, and each time they are reground, of

course, a; to k of the metal of the tool bit had to be removed.

I believe that one possible explanation of the long life of my plated tools is that the cheaper steel bits, that is tool steel bits, have slightly more flexibility than the high speed alloy steel bits, and that, relatively speaking, a piece of softer tool steel compared with the high speed steel, when covered with an extremely hard surface of chromium, presents a hard cutting surface with a, relatively softer cushion, thus minimizing the tendency of the chromium to crack or chip.

It will be understood that I do not Wish to limit the treatment to bits formed of tool steel, but the process and method might well be used on other articles having different characteristics than those outlined above, such as gears, cams, and other articles on which are placed concentrated loads.

This is a continuation-in-part of my application Serial Number 437,882, filed April 6, 1942, which has become abandoned.

Having thus described my invention, what I claim as new and desire to secure by letters Patent is:

1. A method of plating and treating steel metalcutting tools which comprises immersing a portion of a steel tool to be plated in an electrolytic bath containing between about 30 and ounces of chromium trioxide and sulphate in amount equal to about one-hundredth of the weight of amperes per square inch and at a bath temperature between about F. and F. for a period of about 1 to 2 minutes, removing the article from the bath, heating the tool in a heat treatment bath to release hydrogen and decrease the brittleness of said tool, and cooling the article.

2. A method of plating and treating steel metal-cutting tools which comprises immersing a portion of a steel tool to be plated in an electrolytic bath containing chromium trioxide and sulphate, electrodepositing chromium on said tool at a current density between about 0.7 and 3.5 amperes per square inch and at a bath temperature between about 100 and 190 F. for a period of about 1 to 2 minutes, removing the tool from the bath, heating the tool in a heat treatment bath at a temperature of about 350? F., and cooling the tool.

3. A method of plating and treating steel metalcutting tools comprising at least partially immersing a steel tool formed of tool steel in an electroplating bath containing chromium trioxide and sulphate, electrodepositing chromium on said tool at a current density between about 0.7 and 3.5 amperes per square inch for a period of about 1 to 2 minutes to produce a chromium plate not exceeding 0.0001 inch in thickness,

making the tool an anode in said bath for a few seconds, removing the tool from the bath, heating it in hot oil and cooling the tool.

4. A method of plating and -treating steel metal-cutting tools comprising immersing at least a portion of a steel tool in an aqueous electroplating bath containing about 0.5 ounce of sulphate and about 50 ounces of chromium trioxide per gallon, making the tool an anode in said bath for a few seconds to clean the tool anodically, electroplating the tool as a cathode at a current density between about 100 and 400 amperes per square foot for about 1 to 2 minutes, making the tool an anode for a few seconds to remove any beads formed on said tool, removing the tool from the bath, heating it in a hot oil, and cooling the tool.

5. A method of plating and treating steel metal-cutting tools comprising immersing at least a portion of a steel tool in an aqueous electroplating bath containing about 0.33 ounce of sulphate and about 33 ounces of chromium trioxide per gallon, making the tool an anode in said bath for a few seconds to clean the tool anodically, electroplating the tool as a cathode at a current density between about 1 to 3% amperes per square inch for about 1 to 2 minutes, making the tool an anode for a few seconds to remove any beads formed on said tool, removing the tool from the bath, heating it in a hot oil at a temperature of about 350 F. for about one hour, and cooling the tool.

6. A method of plating and treating steelmetal-cutting tools comprising immersing at least a portion of a steel tool in an aqueous electroplating bath containing about 0.5 ounce of sulphate and about ounces of chromium trioxide per gallon, making the tool an anode in said bath for a few seconds to clean the tool anodically, electroplating the tool as a cathode at a current density between about and 400 amperes per square foot and at a temperature of about 150 F. for about 1 to 2 minutes, making the tool an anode for a few seconds to remove any beads formed on said tool, removing the tool from the bath, heating it in a hot oil at about 350 F. for about one hour, and cooling the .tool.

'7. A method of plating and treating steel metal-cutting tools comprising immersing at least a portion of a steel tool in an aqueous electroplating bath containing about 0.33 ounce of sulphate and about 33 ounces of chromium trioxide per gallon, making the tool an anode in said bath for a few seconds to clean the tool anodically, electroplating the tool as a cathode at a current density between about 1 /2 to 3 amperes per square inch and at a temperature of about F. for about 1 to 2 minutes, making the tool an anode for a few seconds to remove any beads formed on said tool, removing th tool from the bath, heating it in a hot oil at about 350 F. for about one hour, and cooling the tool.

AXEL E. LUNDBYE. 

